As is known, in the so-called anthraquinone method for the manufacture of hydrogen peroxide (see the summarizing presentation in "Ullmanns Enzyklopaedie der technischen Chemie", 4th revised and expanded edition, vol. 17, pp. 697-704) an anthraquinone derivative, the reaction carrier, is dissolved in a solvent or solvent mixture and the working solution obtained in this manner is hydrogenated in the presence of a catalyst. A part of the anthraquinone derivative is converted by this step into the corresponding anthrahydroquinone derivative. The hydrogenation catalyst is separated by filtration, and the working solution is reacted with oxygen or with an oxygen-containing gas (usually air) to convert the anthrahydroquinone derivative to the anthraquinone derivative with concurrent formation of hydrogen peroxide.
The hydrogen peroxide dissolved in the working solution is extracted with water and the working solution can be recirculated to the hydrogenation stage. Continuous repetition of the individual steps results in a cyclic process in which hydrogen peroxide is synthesized from the gases hydrogen and oxygen.
Regardless of what industrial device is used to extract the hydrogen peroxide, two phases are always obtained after the extraction stage, the working solution phase (raffinate) with reduced H.sub.2 O.sub.2 content and the aqueous hydrogen peroxide phase (extract).
Each phase contains a very finely dispersed portion of the other phase in small amounts, that is, very fine droplets of a diluted aqueous hydrogen peroxide are contained in the working solution phase and small amounts of working solution droplets are dispersed in the aqueous hydrogen peroxide phase.
Usually, the working solution phase is passed through conventional coagulators and separators, the so-called "water separators" in order to separate out the aqueous dispersed phase. The aqueous phase separated out in the "water separators" is a diluted aqueous hydrogen peroxide solution.
A number of procedures have been suggested in order to purify the aqueous hydrogen peroxide extract.
Thus, for example, the purification of the aqueous H.sub.2 O.sub.2 solutions may be performed by means of an adsorptive treatment. The following adsorbents have been proposed: Activated carbon (U.S. Pat. No. 2,919,975), activated carbon in the form of finely distributed wood charcoal, MgO, freshly precipitated Al(OH).sub.3 or Mg(OH).sub.2 (British Pat. No. 817,556), an activated carbon partially deactivated by means of the adsorption of organic substances which are inert with respect to H.sub.2 O.sub.2 (DE-PS No. 15 67 814), ethylene polymerizates with a molecular weight over 2000 (GB No. 794,433), water-insoluble, solid, non-polymeric organic substances having molecular weights between approximately 170 and 1000 (DE-PS No. 11 08 191) and porous synthetic resins which are free of chemical functions (DE-OS No. 17 92 177).
Since activated carbon decomposes the hydrogen peroxide to be purified, the treatment is preferably performed at low temperatures. In addition, as the purification proceeds, the adsorbents are charged with the impurities and must be regenerated in a separate circuit with the aid of solvents.
It is also known (U.S. Pat. No. 3,043,666 - FMC) that the aqueous H.sub.2 O.sub.2 solution can first be treated with a selective solvent for quinones and that the raffinate which is obtained from this step can be heated in the presence of a stabilizer until a coloration occurs. The dissolved organic constituents are oxidized by hydrogen peroxide and are subsequently extracted and finely distilled. These measures are so expensive that they are only justified in the case of special quality products.
In other purification methods the aqueous hydrogen peroxide extract is extracted with a solvent. The solvent used can be an inert liquid hydrocarbon with a boiling point at atmospheric pressure of not above 145.degree. C. (DE. No. 10 36 225) or hydrocarbons with boiling points between 50.degree. and 120.degree. C. and solubilities in water under 0.1% can be used (Japanese Pat. No. 35-2361). Even certain chlorinated hydrocarbons have been suggested (DE-AS No. 11 35 866). Solvent residues have to be stripped from the H.sub.2 O.sub.2 after the purification in the extractive purification methods which make use of a low-boiling solvent; furthermore, the charged solvent must be regenerated in a separate circuit, which is thus expensive. Finally, many of the solvents suggested have a low flash point.
It should be possible to avoid the disadvantages if the purification stage is performed in a solvent mixture consisting of aromatic substances with a boiling range of 145.degree.-200.degree. C. (British Pat. No. 841,323).
It is also known that a mixture of aromatic hydrocarbons with a boiling point above 145.degree. C. and methylcyclohexylacetate in certain proportions can be used to purify the raw aqueous hydrogen peroxide solutions. (DE-AS No. 14 67 091).
According to the state of the art, the extraction of the impurities is performed in spray columns, sieve-plate columns or in columns filled with filling bodies according to the countercurrent method. Drops of entrained solvent are separated out of the aqueous phase in a succeeding delaying section.
As is known, the mass transfer increases in an extraction process as the phase interface surface increases; however, on the other hand, the separation of a two-phase mixture is facilitated by using larger drops. These two factors which counteract each other limit the yield in an extractive purification of aqueous hydrogen peroxide solutions with solvents in columns.